The proposed research will demonstrate the feasibility of constructing a quantitative instrument independent diagnostic device for determination of theophylline in human saliva. Such a device is intended for medical professionals to permit them to better control and monitor treatments involving theophylline, especially asthma. Like EMIT assays, the device will utilize competitive binding of theophylline and an analyte-enzyme conjugate to a monoclonal anti-theophylline antibody. Unlike EMIT, the device utilizes the principles of analog-to-digital color control chemistry to give direct readout of theophylline concentration without the use of instruments or conversion charts. By using saliva as specimen, this assay will permit convenient, repeated assessment of theophylline status. Its availability should encourage theophylline dosage by individual titration, with a concomitant increase in the effectiveness of treatment and a decrease in side effects and expense related to overdose.